The present invention is directed to the fluid driven turbine art and, in particular, to a two-stage fluid driven turbine which is capable of high efficiency operation over a broad range of drive fluid velocities.
Numerous turbine configurations are known to the prior art. Turbines are commonly employed to convert a fluid flow to rotation of a drive shaft. A particular application for a turbine is in the testing of fans, pumps or propellers for use in aircraft or other aerospace applications. Ideally, the propeller of fan under test should be driven at speeds normally expected in its intended application. Further, the test structure behind the fan or propeller should be aerodynamically similar to the structure encountered in the actual application, such that flow patterns past the fan or propeller can be simulated. In addition, the drive source to the fan or propeller should be sufficiently quiet such that noise levels produced by the fan or propeller can be accurately measured.
Heretofore, the drives for testing fans and propellers have suffered from numerous deficiencies. For example, hot gas turbine drives have been used in fan and propeller testing, but the size of the hot gas turbines required to drive the fans or propellers to realistic levels has been so large that such turbines have blocked airflow behind the fan or propeller, thereby obstructing airflow measurements. In addition, hot gas turbines are noisy, tending to mask the noise from the fan or propeller under test.
A further problem associated with hot gas turbines is that they are designed to operate within a specific RPM range and do not provide a high output for speeds "off" this range. As such, the use of hot gas turbines has proved inappropriate for testing fans or propellers over their entire operating range.
Additionally, electric motors have been employed in propeller and fan testing. Again, however, the electric motors required to drive fans and propellers to realistic levels have been so large that they, also, block airflow behind the fan or propeller. While attempts have been made in locating the motor in an adjacent room and routing drive shafts with gearing to the propeller, the losses encountered in such constructions have proved intolerable.
The is a long felt need in the propeller and fan testing art, therefore, for a turbine design which exhibits a high output over a broad RPM operating range and which is both quiet and relatively small in configuration.